diff --git a/replicate/prediction.py b/replicate/prediction.py
index 84afaae9..54f5db66 100644
--- a/replicate/prediction.py
+++ b/replicate/prediction.py
@@ -52,10 +52,24 @@ def cancel(self):
 class PredictionCollection(Collection):
     model = Prediction
 
-    def create(self, version: Version, input: Dict[str, Any]) -> Prediction:
+    def create(
+        self,
+        version: Version,
+        input: Dict[str, Any],
+        webhook_completed: Optional[str] = None,
+    ) -> Prediction:
         input = encode_json(input, upload_file=upload_file)
+        body = {
+            "version": version.id,
+            "input": input,
+        }
+        if webhook_completed is not None:
+            body["webhook_completed"] = webhook_completed
+
         resp = self._client._request(
-            "POST", "/v1/predictions", json={"version": version.id, "input": input}
+            "POST",
+            "/v1/predictions",
+            json=body,
         )
         obj = resp.json()
         obj["version"] = version
diff --git a/tests/test_prediction.py b/tests/test_prediction.py
index 47c1dceb..4d0dcef8 100644
--- a/tests/test_prediction.py
+++ b/tests/test_prediction.py
@@ -13,7 +13,13 @@ def test_cancel():
     responses.post(
         "https://api.replicate.com/v1/predictions",
         match=[
-            matchers.json_params_matcher({"version": "v1", "input": {"text": "world"}})
+            matchers.json_params_matcher(
+                {
+                    "version": "v1",
+                    "input": {"text": "world"},
+                    "webhook_completed": "https://example.com/webhook",
+                }
+            ),
         ],
         json={
             "id": "p1",
@@ -33,7 +39,11 @@ def test_cancel():
         },
     )
 
-    prediction = client.predictions.create(version=version, input={"text": "world"})
+    prediction = client.predictions.create(
+        version=version,
+        input={"text": "world"},
+        webhook_completed="https://example.com/webhook",
+    )
 
     rsp = responses.post("https://api.replicate.com/v1/predictions/p1/cancel", json={})
     prediction.cancel()